The head of the Police Federation today said "a touch of ideology" and bad advice to government from thinktanks had left the police service facing cuts that could leave up to 40,000 officers out of a job.

Paul McKeever, the federation's chairman, warned that some forces would be "devastated" and said the proposed cuts would leave the public less safe.

He said the most vulnerable in society would be worst hit, adding: "It is likely that crime levels will go up."

The comments increased the pressure on the government from the federation, some of whose leaders believe senior officers have not been vocal enough in fighting the cuts.

The organisation's strategy is to spell out what it says would be the effects of a 25% cut to the police budget in the hope that adverse public reaction would make the government treat policing as a special case – similar to the health and defence budgets, which will be spared the worst of the cuts.

The federation represents rank and file officers in England and Wales, and McKeever warned that more than a quarter of police officers faced losing their jobs. Thousands of civilian police staff also faced the axe, he said.

Figures from the federation show eight forces have already announced plans that would see 3,500 police officers scrapped.

It said 1,000 police officers would be lost in the West Midlands, around 10% of the total. Greater Manchester's public order and counter-terrorism unit would be hit, and units across the country tackling anti-social behaviour, burglary and violent crime would become less able to keep the public safe.

McKeever said the government had been badly advised. "I think there is a touch of ideology there, a belief in the theory they have been given," he said.

"Some people in business consulting and the thinktank world think you can make 25% savings by saving paper clips and by reorganising. But to think you can make 25% savings and have the same level of service is utter nonsense."

Next week, the Police Superintendents' Association conference will outline the dangers the cuts could bring.

McKeever said some police chiefs had none done enough to protect the service, adding: "We have not seen a lot of resistance from the senior echelons. Some seem to be frozen like rabbits in the headlights."

In a statement, chief constable Grahame Maxwell, the Association of Chief Police Officers' (Acpo) lead for finance and resources, said: "The reality is that the scale of cuts currently being discussed is so significant that 'protecting the frontline' cannot mean 'maintaining the frontline at current levels'.

"We will need honest conversations with politicians and the public about what services policing continues to deliver, and what stops."

The policing minister, Nick Herbert, said: "I understand the Police Federation wants to make its case and protect every job, but we must be careful not to frighten the public.

"Police forces can make savings. They can become more efficient. They can share services and procure equipment better."

The Home Office said future funding for the police would be decided by the spending review, which is due to report in October.

A spokesman said the police service would need to play its part in cutting the deficit.